Publication: ASSESSING THE EFFECTS OF HEAVY METALS ON OXIDATIVE STRESS AND METABOLOMIC PROFILES OF MICROALGAE ISOLATED FROM SIGNY ISLAND, ANTARCTICA
Date
2020
Authors
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Publisher
International Medical University
Abstract
Increasing human activities has led to anthropogenic contamination of heavy metals in the environment of Antarctica. Microalgae, the primary producers of the food chain, are the first target affected by heavy metal pollution. The primary aim of this study was to assess the toxic effects of copper (Cu) and lead (Pb) on microalgae isolated from Signy Island, Antarctica, with emphasis on their oxidative stress response and metabolomic profiles. In addition, the heavy metal contents and occurrence of microalgae in the soils from differently impacted sites of Signy Island were investigated. A total of 29 taxa of microalgae from Bacillariophyta, Chlorophyta, Cyanobacteria, and Tribophyta were recorded from cultured materials derived from the soil samples collected from Signy Island. The soil contents of 14 metals (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, and Zn) from five sampling sites (Berntsen Point, Gourlay Peninsula, Jane Col, North Point, and Pumphouse Lake) were determined. Results showed that the Cu content was highest in Gourlay Peninsula (135.36 ± 71.99 μg/g) while the Pb content was highest in Berntsen Point (14.78 ± 23.91 μg/g).
Twenty-two unialgal strains were isolated. Morphological analysis using light microscope showed that three of the unialgal isolates were from the genus Coccomyxa and 19 isolates were from the genus Chlorella and allies. Phylogenetic analysis showed that the isolates were clustered in separate clades consisting of Coccomyxa subellipsoidea, Micractinium inermum, Chlorella sp., and Chlorella vulgaris.
Micractinium inermum BP-33 isolated from high Pb site (Cu=1.523 μg/g; Pb=127.643 μg/g) and C. vulgaris GP24 isolated from high Cu site (Cu=119.942 μg/g; Pb=0.893 μg/g) were chosen for 10-day Cu and Pb toxicity testing. Micractinium inermum BP-33 was more sensitive to both Cu and Pb while C. vulgaris GP24 was more resistant to both metals. Exposure of the microalgae to the metals resulted in decreased chlorophyll a, chlorophyll b, and carotenoid contents.
The microalgae exposed to the metals for 4 and 10 days showed increased cell granularity, accumulation of large amounts of starch granules, abundant vacuoles with electron-dense polyphosphate bodies, and alteration in chloroplast structure. The reactive oxygen species (ROS) levels of M. inermum BP-33 exposed to Cu were similar to the control while superoxide dismutase (SOD) and catalase (CAT) activities increased significantly (P<0.05). The ROS levels in Micractinium inermum BP-33 exposed to Pb were significantly lower (P<0.05) than the control. In terms of antioxidant enzyme response, there was an increase in SOD activity but no significant change in CAT activity was observed. In C. vulgarisGP24, the ROS levels were significantly lower (P<0.05) than the control when exposed to Cu at EC50. A decrease in SOD activity and an increase in CAT activity were also observed. In comparison, the ROS levels in C. vulgarisGP24 exposed to Pb at EC10were significantly higher (P<0.05) than the control, with significant increase (P<0.05) in both SOD and CAT activities.
The metabolic responses of microalgae after exposure to Cu and Pb for 4 and 10 days were analysed using 1H NMR spectroscopy. Subsequent PLS-DA scores plot showed that Cu and Pb-treated cells were clearly distinct from the control. The covariance plots calculated using permutation test revealed that the discrimination pattern in PLS-DA plots were mainly influenced by carbohydrates, some amino acids and organic osmolytes. The highest number of metabolite changes were detected in M. inermum BP-33 after exposure to Pb for 10 days (9 up-regulated; 22 down-regulated), while the least number of significant metabolites changes was detected in C. vulgaris GP24 after exposure to Cu for 10 days (2 up-regulated). Metabolites that confer potential oxidative protection such as glutathione, malate, myo-inositol, inosine, proline, and taurine were detected in the microalgae exposed to heavy metals. Glutathione and malate were up-regulated in both microalgae exposed to Pb while myo-inositol and inosine were up-regulated in M. inermum BP-33 after being exposed to Pb for 10 days. In addition, proline was up-regulated in M. inermum BP-33 on day 10 after exposure to Pb while in C. vulgaris GP24, this occurred on day 4. Down-regulation of taurine was observed in both microalgae after being exposed to Cu and Pb for 4 days.
In conclusion, the findings of this study suggested that heavy metals could affect the occurrence of soil microalgae on Signy Island. Heavy metals could disrupt the growth, photosynthetic pigments, and cellular features of microalgae. Heavy metals could also disrupt oxidative balance of microalgae, trigger the increase in antioxidant enzymes activity, and alter the metabolites in the microalgae.
Description
Keywords
Microalgae, Metals, Heavy, Oxidative Stress, Metabolomics, Copper, Lead